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Einstein Gravitational-wave Telescope EINSTEIN TELESCOPE ON THE NATIONAL ROADMAP FOR LARGE-SCALE RESEARCH FACILITIES Conceptual diagram of the Einstein Telescope facility. Three detectors are configured in a triangular topology, and each detector consists of two interferometers. The 10 km arms of the observatory are housed underground to suppress seismic and gravity-gradient noise. Optical components are placed in an ultra-high vacuum and cryogenic environment. This proposal makes the case to realize Einstein Telescope in the Netherlands. 1/21 KNAW-Agenda Grootschalige Onderzoeksfaciliteiten Format nadere uitwerking van een ingezonden voorstel I. GENERAL INFORMATION Acronym ET Name infrastructure Einstein Telescope Main applicant Prof.dr. Jo van den Brand Also contact person Organisation Nikhef and VU University Amsterdam Function Professor Address Science Park 105, 1098 GW Amsterdam, The Netherlands Phone +31 620 539 484 Email [email protected] Co applicants: Henk Jan Bulten, Nikhef and VU University Amsterdam Martin van Beuzekom, Nikhef Chris Van Den Broeck, Nikhef Niels van Bakel, Nikhef Alessandro Bertolini, Nikhef Jan Willem van Holten, Nikhef and Leiden University Paul Groot, Radboud University Gijs Nelemans, Radboud University Summary Einstein Telescope is a new infrastructure project that will bring Europe to the forefront of the most promising new development in our quest to fully understand the origin and evolution of the Universe, the emergence of the field of Gravitational Wave Astronomy. Gravitation is the least understood fundamental force of nature. Challenges include discovery of new sources and exploitation of gravitational waves, experimental constraints on the corresponding quantum (graviton) and the development of an observation-based field of research on quantum gravity. We propose that Einstein Telescope is realized in the Netherlands (part of Euregio Maas-Rhein) and will be an underground international facility containing cryogenic interferometers with 10 km arms. We propose a phased approach where Phase I will allow qualification of sites in the Netherlands. After successful site selection, Phase II will involve construction, followed by exploitation in Phase III. Keywords Gravitational waves, fundamental physics, astronomy, astrophysics, black holes, early Universe, data analysis, laser interferometry, computing 2/21 II. PROPOSAL A. SCIENCE AND TECHNICAL CASE Einstein Telescope in the Netherlands Einstein Telescope (ET) is a new infrastructure project that will advance our understanding of the origin and evolution of the Universe by the detection and exploitation of gravitational waves. We propose that ET is realized in the Netherlands (as part of Euregio Maas-Rhein). It will be an advanced underground international facility containing cryogenic laser interferometers with 10 km arms. The Einstein gravitational–wave Telescope will be an observatory of the third generation aiming to reach a sensitivity for gravitational wave signals emitted by astrophysical and cosmological sources about a factor of 10 better than the design sensitivity of the current second generation LIGO and Virgo advanced detectors, and will cover an extended frequency range from 2 to 104 Hz. Recently, the LIGO Virgo Collaboration has detected the first gravitational wave events from merging black holes. With its outstanding sensitivity, the ET observatory will open the era of routine gravitational wave astronomy with hundred thousands of detections per year. ET will be realized in a phased approach. In Phase 0 a conceptual design study for ET was carried out in the FP7 framework call (see http://www.et-gw.eu/etdsdocument ). An R&D proposal ET was approved by ApPEC in 2012. Moreover, a Governing Council was instituted and a scientific collaboration was organized through the ET Science Team. Furthermore, ET was included on various roadmaps. At present we are in Phase 1. An international community for ET exists with the required expertise to realize this facility. To organize and focus this community an integration proposal is being prepared that will be submitted to Horizon 2020 in 2016. In addition various countries have begun a systematic studies of sites to host the observatory. The hosting of ET in the Netherlands (as part of Euregio Maas-Rhein) would have enormous benefits for the Dutch science community, society, and the Limburg region. Phase I of our proposal involves a detailed investigation of possible sites in the Netherlands to construct ET. Approval of Phase I would allow Dutch scientists to prepare the case for ET in the Netherlands. Phase 2 involves construction, while scientific exploitation of the observatory occurs in Phase 3. For millennia the Universe has been studied with light and other forms of electromagnetic radiation. ET will open a new window on the Universe and since gravitational waves penetrate all regions of time and space with almost no attenuation, ET can sense waves from the densest regions of matter, the earliest stages of the Big Bang, and the most extreme warpings of spacetime near black holes. Science Case ET will feature advanced ground-based interferometers that will see gravitational wave observations firmly embedded in the wider field of astronomy and astrophysics. Enhancing detector performances beyond those achievable with current instruments will make it possible to continuously observe the distant, dark, dense and catastrophic Universe. Detectors capable of observing binary black hole (BBH) mergers will have an enormous impact in several key areas of astrophysics, cosmology and fundamental physics. 3/21 Targeted sources of gravitational waves: ET is primarily conceived to be a broadband detector, with good sensitivity over a significant part of the frequency range of 2–104 Hz. There are many classes of potential sources that are of great interest over this range. Binary neutron stars will sweep through the detector band from 2 Hz to 4 kHz, the signal lasting for several days as the system inspirals to a catastrophic merger event. The long observation times will make it possible to predict the location of the source and the precise time (to within milliseconds) when the system would coalesce, thereby facilitating simultaneous observation of the final merger of the two neutron stars using all windows of astronomical observation. Binary black holes will also last for several hours, up to a day, again making it possible to observe such events using optical, radio and other telescopes. Transient astronomical sources that are powerful emitters of high energy gamma-ray bursts and X-rays could also be visible in the gravitational window and reveal the inner structure of such sources. For instance, by observing the fluid modes of compact objects it would be possible to measure the equation of state of matter under extreme environments of gravity, magnetic field, temperature, etc. With a network of interferometers of capabilities similar to ET it should be possible to measure a stochastic gravitational wave background whose energy density is as small as 10–11 times that of the critical density of the Universe. ET will provide a new window on the Universe and can be expected to detect sources that have never been seen or imagined before. Volume coverage and completeness of surveys: ET can basically be regarded as a survey telescope. ET will be able to constantly watch the entire gravitational sky, pointing of sources made possible either with the help of data from a network of three or more detectors, e.g. in the US and Australia, or by virtue of the modulation in the signal caused due to the detector’s motion relative to the source. Indeed, at its best conceived configuration ET will observe binary neutron star mergers within a red- shift of z = 2, binary black hole sources to a distance of z = 17, and all millisecond period neutron stars in the Galaxy with ellipticities larger than 10–8. Strong field tests of Einstein’s gravity: Recent research has shown that some of the strong field tests of general relativity are possible only with the help of binary inspiral events that have signal-to-noise ratios (SNRs) in excess of about 100. Events with such high SNRs are not thought to occur frequently enough in current detectors. ET should be able to observe binary inspirals with SNRs of 100s about once each year. A single ‘gold-plated’ event will help explore the various nonlinearities of general relativity in ways that would never be possible with other terrestrial or solar-system experiments or radio binary-pulsar observations. Moreover, the higher harmonics that are present in the waveform will reveal the nature of the spacetime geometry in strong gravitational fields (as would result when compact stars merge) and help us formulate fundamental questions about the end-product of a gravitational collapse, Black hole mergers are the most powerful events in the Universe, and their if it is a black hole as gravitational waves allow stringent tests of general relativity. 4/21 predicted by general relativity or a more exotic object such as a naked singularity – a state in which a highly singular region of spacetime geometry is not shrouded in a horizon. Astronomy: ET should observe a variety of different sources that should help resolve decades-old astronomy questions. The most important one amongst these is the origin of gamma-ray bursts (GRBs), pioneered by the Dutch astronomer Jan van Paradijs, which have remained an enigma nearly four decades after their serendipitous discovery in the 60’s and 70’s. Because of ET’s sensitivity to binary inspirals at high red-shifts, it should be possible to pin down the origin of GRBs and to confirm or rule out the association of binaries of NS-NS/BH and systematically study and understand different classes of GRBs. At the high frequency end of ET’s sensitivity, oscillations of neutron stars could be used to carry out asteroseismology and study the equation-of-state and the internal structure of matter at extreme environs of density, temperature and magnetic fields. Finally, the large amount of NS and BH mergers will provide accurate tests of the preceding binary evolution, which includes very uncertain phases.
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